1. Field of the Invention
This invention relates in general to earth-boring rotary cone drill bits and in particular to a protective device for protecting the seal of each cone from damage due to debris.
2. Description of Related Art
Earth-boring bits of the type described herein include a bit body having at least one bearing pin, normally three, and a cone rotatably mounted to each bearing pin. Each cone includes cutting elements for engaging the earth formation as the bit body rotates. The bearing spaces between the cavity of the cone and the bearing pin are typically filled with a lubricant. A seal is located near the mouth of the cone cavity for the purpose of sealing lubricant from drilling fluid.
During typical drilling operations, debris, whether it originates from the drill bit bearing or the bore hole, can find its way to the seal and cause wear, which in turn can eventually lead to the failure of the seal. One type of seal includes an elastomeric member having an inner diameter in sliding engagement with the bearing pin and an outer diameter that is normally in static engagement with the cone. This type of seal can form a nip area with the bearing pin and allows debris to accumulate near and migrate into the sealing interface. The accumulated debris can cause wear and leakage.
Another type of seal used in drill bits employs primary metal-to-metal face seals that are energized by an elastomeric ring. One type of seal assembly employs a secondary elastomeric seal exterior of the energizer ring to protect the primary seal. The secondary seal takes up precious space, and the assembly requires pressure compensation for the space between the two seals.
Other designs use an elastomeric ring that has a more wear-resistant elastomeric layer upon the inner diameter. The more wear-resistant layer may include a different elastomer, or it may be made up of a wear-resistant fabric. This arrangement does not necessarily prevent the migration of debris to the primary, and does not prevent wear and leakage.
Thus, there exists a need to provide an improved seal for a roller cone drill bit whereby wear and leakage may be minimized.